Values
Off
Will not cast any shadows.
On
Will cast shadows from all visible faces in the GeometryInstance.
Will take culling into account, so faces not being rendered will not be taken into account when shadow casting.
DoubleSided
Will cast shadows from all visible faces in the GeometryInstance.
Will not take culling into account, so all faces will be taken into account when shadow casting.
ShadowsOnly
Will only show the shadows casted from this object.
In other words, the actual mesh will not be visible, only the shadows casted from the mesh will be.